1. Field of the Invention
The present invention relates to a semiconductor device, and a method of manufacturing the same.
2. Discussion of the Background
In a device where a gate insulator film is used as a tunnel insulator film as represented by an electrically erasable and programmable read-only memory (EEPROM), high electric fields exceeding 10 MV/cm are applied to the gate oxide film in order to write and erase information. Further, gate insulator films employed as MOSFETs of logic devices are subjected to even higher electric fields requiring microfabrication of the MOSFET in order to maintain performance.
Such a gate insulator film requires a high reliability due to the high electric field applied thereto and the high energy of the electrons transiting the electric field. By way of example, there is a problem that, when an electrical stress is applied, defects are created in the gate insulator film. Since the defects created form seeds for inducing dielectric breakdown, or the defects created induce a low electric field leakage current called a “stress-induced leakage current” (SILC). Diminution of defect creation governs the reliability of the semiconductor device operating as a gate insulator film. Regarding a mechanism in which such defects appear, hydrogen atoms existing in the film are related to defect generation. Therefore, a technique has heretofore been proposed in which hydrogen in the gate insulator film is substituted with deuterium or tritium, being an isotope of hydrogen, thereby to diminish the appearance of defects. A method for introducing deuterium into a gate insulator film is, for example, a method in which, during annealing of a transistor, the gate insulator film is exposed to an atmosphere of a nitrogen-diluted deuterium gas or exposed to an atmosphere of 100% deuterium gas, instead of annealing thereof in a nitrogen-diluted hydrogen gas. There is also a method in which a silicon substrate is exposed to deuterium oxide (D2O), thereby to form a gate oxide film (Official Gazette of Japanese Patent Laid-Open No. 12609/1998), or a method in which a gate oxide film is nitrided by exposing the gate oxide film to deuterated ammonia (ND3), thereby to form a silicon oxynitride film containing deuterium (Official Gazette of Japanese Patent Laid-Open No. 274489/1999).